Lots of unpleasant things from nuclear war to asteroid impacts
could destroy life on Earth.
But what about Earth itself?
Will anything ever destroy this planet?
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The physics of breaking something, including planets,
is pretty straightforward-- just add enough energy
to the individual chunks to overcome the attractive forces
gluing them together.
Now in the case of Earth, the main glue
is the collective gravity of almost six septillion kilograms
of mass.
So separating the chunks takes an obscene amount of energy.
How much?
About as much solar energy as a whole Earth
receives over 40 million years.
Now if you just want to split Earth in half,
you get a bit of a discount-- only 16 million years
worth of sunshine.
So realistically, could anything deliver that much energy
to Earth and end the planet as we know it?
Let's review some possibilities, starting
with one that has probably crossed your mind
at some point-- nukes.
Could we nuke the planet to bits?
I looked up the most powerful nuke ever built.
It was the Soviet Tsar-Bomb from the 1960s.
When test detonated, it released the equivalent
of 50 megatons of TNT, give or take.
That was enough energy to level everything
for more than 20 miles in every direction in northern Russia
and even shattered windows hundreds of miles
away in Finland.
So I did some arithmetic.
To wreck the planet, you'd need-- are you ready
for this-- over one quadrillion Tsar-Bombs.
Is there even enough mineable uranium on Earth for that?
Almost certainly no, but even if there was,
humanity has neither the time nor inclination to make
one quadrillion of anything.
I mean, all of YouTube is estimated
to host only a few hundred million videos in total.
So can we nuke the Earth to a barren wasteland?
Absolutely.
But can we nuke it to pieces?
Not even close.
So let's move on to the next obvious suspect-- asteroids.
Sorry, kids, also not enough energy.
Let me give you some context.
The supposed dinosaur killer was the equivalent
of about one million Tsar-Bomb detonations, which is huge
but still only one billionth of the energy needed
to blow up a planet.
Even 4-Vesta, the biggest object that's
still classified as an asteroid, would only
care about half a percent of the required energy.
The issue is speed.
To destroy Earth, 4-Vesta would have
to hurtle toward it at 700 kilometers per second--
or fast enough to get from New York to LA
in under five seconds.
But asteroids orbit the sun about 35 times slower
than that.
In fact, a head-on collision between Earth
and any solar system object deflected into our path
will top out at a mere 70 to 80 kilometers per second.
Now with those speeds, an object could only carry enough energy
to destroy Earth if it had a huge mass,
which asteroids don't.
Planets, on the other hand, do-- which brings
me to colliding with Mars.
Now, I know what you're thinking.
Mars orbit outside Earth's orbit,
so how could they collide?
Well, Earth and Mars' field gravitational
pulls not just from the sun, but also from the other plants--
and from big asteroids too.
Now, those extra tugs are tiny.
But if everything lines up just right, then over billions
of years, they could have a sizable cumulative effect
and distort those orbits.
Emphasis on could.
In a paper linked in the description,
some French physicists ran 2,500 distinct simulations
of the solar system's evolution over the next few billion
years.
All they changed from one initial set up to another
was Mercury's current position by about a meter.
OK, you know that diorama of the solar system
you made back in fifth grade?
99% of the simulation stay faithful to that.
But in 1%, the inner planet orbits
stretch out after about three billion years and Earth
starts doing drive-bys of Venus and Mars.
In one simulation, about four billion years from now,
Earth and Mars actually collide with enough energy
to do serious structural damage.
So a Martian collision is possible, but is it likely?
That's a hard question to answer.
As in weather forecasting, you have a butterfly effect
situation that's highly unpredictable.
All we can say for now is that death
by interplanetary headbutt isn't ruled out.
Of course, hulk smash isn't the only way to destroy something.
You can also cook it into oblivion.
For instance, if Earth enters the sun.
All right, in about five billion years,
the sun will begin its transition
into a red giant-- inflating until it
becomes slightly larger than Earth's entire current orbit.
Now if Earth stays where it is now, during that growth spurt,
we get swallowed up.
And it's game over.
See, another paper in the description
works out that an Earth-like planet in a solar atmosphere
would vaporize after a few million years.
So the Earth is toast, right?
Well, it's not that simple because there's
a competing effect.
See, the growing sun will also develop a stronger solar wind
that sprays a lot of the sun's material out into space.
In the process, the sun will lose a lot of mass
and a lot of gravitational pull, causing Earth's orbit
to actually grow.
For decades, whether Earth will be swallowed by the sun or not
has been too close to call.
Astronomers have gone back and forth on the answer.
But the best recent simulations show
that Earth will end up just inside the sun and fry.
Now, as always, it's prudent to see whether that answer holds
up under future simulations.
But slow roasting into iron vapor seems fairly unavoidable.
Which is a shame, because it means
earth is unlikely to face one final destruction
scenario that we're going to talk about anyway
just because of the sheer awesomeness factor-- death
by expanding universe.
Here's the deal.
Currently, the universe is expanding
and currently that expansion is speeding
up due to an unidentified material permeating
the cosmos that physicists have dubbed "dark energy".
It's useful to think of that process-- the expansion--
not as galaxies flying apart through space, but instead
as the space between distant galaxies
stretching, like spandex.
Note that the Earth and you and I stay in one piece
because the space inside galaxies
is not stretching-- at least not yet.
See, ESA's Planck satellite measured, among other things,
a few properties of this mysterious dark energy
that can be used to do some space expansion forecasting.
And those measurements, while not conclusive,
do allow for a scenario that physicists call The Big Rip.
Based on Planck's 2014 data, sometime between 100 billion
and a few trillion years from now,
space could start to stretch-- not just at faster rates,
but on smaller and smaller scales.
Inside galaxies, then inside planetary systems,
inside planets themselves until literally,
everything in a universe is ripped apart
by stretching space-- atoms, nuclei,
individual protons, everything.
Now, disclaimer-- I'm not saying The Big Rip is inevitable.
A Ripless future is also within Planck's margin of error
and The Big Rip scenario has other issues
that make a lot of physicists, including me, skeptical.
Still, if Planck's best-fit numbers
do stand up to further experiments,
I mean, having your atoms disassembled
by space itself would be a pretty epic way to go.
So there it is.
Being ripped to pieces like Braveheart
would be totally sweet, but Earth will probably
burn up like Joan of Arc-- which is still going out in style.
Now, how would you prefer to have Earth meet its maker?
Let me know in the comments along
with any other viable scenarios for Earth destruction
that I might have overlooked-- and no, the Death Star is not
a viable scenario.
We'll see what you all came up with on the next episode
of "Space Time".
Last time, we talked about occupying Venus,
and you guys had a lot to say.
Viridis Arborem pointed out that Venus also
inspired a martial arts style-- Venutian
Aikido-- used by the third Doctor from Doctor Who.
I'm kind of an old-school Whovian,
so it cut deep that I missed that one.
Good eye.
Katherine Daniel and lots of other people
point out that it's not necessarily either/or
between Venus and Mars.
I fully agree.
But we're going to have to do one of them first,
and it's a question of which is more feasible.
Zevin X points out that the real problem might be planetism.
Maybe we should be building floating colonies in space.
That would be great, but it's way beyond current technology.
Quite Likely points out that we don't actually know how bad
Martian gravity will be for humans, and we don't.
That's true.
I only said that on Venus, it would be much less of an issue.
And for everyone who argued that exercise alone
can recover the bone density astronauts
lose in space-- it can recover the density,
but the structural integrity seems
to be damaged in a permanent way that we don't yet
know how to fix.
James Roach and a lot of people on the Reddit thread
bring up the sulfuric acid in the atmosphere.
Look, there's not that much sulfuric acid
in the atmosphere.
It's droplets.
There's a lot of sulfur dioxide, but the sulfuric acid
is a tiny fraction of a percent of the entire Venutian
atmosphere.
All I said is that at those levels, it might be manageable.
And to Justin Stein, thanks for generally helping people
keep their physics and their facts straight.
We appreciate the help.
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